In the field of medicine, radiation may be used for diagnostic, therapeutic and palliative purposes. Therapeutic use of radiation such as x-rays and y-rays typically involves using these rays to eradicate malignant cells. Conventional radiation treatment systems used for medical treatment, such as the linear accelerators that produce high-energy x-rays, utilize a remote radiation source external to the targeted tissue. A beam of radiation is directed at the target area, for example a malignant tumor inside the body of a patient. The x-rays penetrate the patient's body tissue and deliver x-ray radiation to the cancer cells, usually seated deep inside the body. This type of treatment is referred to as teletherapy because the radiation source is located at some distance from the target. This treatment suffers from the disadvantage that tissue disposed between the radiation source and the target is exposed to radiation. To reach the cancer cells, the x-rays from an external radiation source must usually penetrate through normal surrounding tissues. Non-cancerous tissues and organs are thus also damaged by the penetrating x-ray radiation.
Brachytherapy, on the other hand, is a form of treatment in which the source of radiation is located close to, or in some cases within, the area receiving treatment. Brachytherapy, a word derived from the ancient Greek word for close (“brachy”), offers a significant advantage over teletherapy, because the radiation is applied primarily to treat only a predefined tissue volume, without significantly affecting the tissue adjacent to the treated volume. The term brachytherapy is commonly used to describe the use of “seeds,” i.e. encapsulated radioactive isotopes which can be placed directly within or adjacent the target tissue to be treated. Handling and disposal of such radioisotopes, however, may impose considerable hazards to both the handling personnel and the environment.
The term “x-ray brachytherapy” is defined for purposes of this application as x-ray radiation treatment in which the x-ray source is located close to or within the area receiving treatment. An x-ray brachytherapy system, which utilizes a miniaturized low power radiation source that can be inserted into, and activated from within, a patient's body is disclosed in U.S. Pat. No. 5,153,900 issued to Nomikos et al. (the “'900 patent”), U.S. Pat. No. 5,369,679 to Sliski et al. (the “'679 patent”), U.S. Pat. No. 5,422,926 to Smith et al. (the “'926 patent”), and U.S. Pat. No. 5,428,658 to Oettinger et al. (the “'658 patent”), all owned by the assignee of the present application, all of which are hereby incorporated by reference. The x-ray brachytherapy systems disclosed in the above-referenced patents include miniaturized, insertable x-ray probes that are capable of controllably producing and delivering low power x-ray radiation, while positioned within or in proximity to a predetermined region to be irradiated. In this way, x-ray radiation need not pass through the patient's skin, bone, or other tissue prior to reaching the target tissue. The probe may be fully or partially implanted into, or surface-mounted onto a desired area, within a treatment region of a patient. The insertable probe emits low power x-rays from a nominal, or effective “point” source located within or adjacent to the desired region to be irradiated, so that substantially only the desired region is irradiated, while irradiation of other regions are minimized. X-ray brachytherapy offers the advantages of brachytherapy, while avoiding the use and handling of radioisotopes. Also, x-ray brachytherapy allows the operator to control over time the dosage of the delivered x-ray radiation.
In oncology, x-ray brachytherapy treatment generally involves positioning the insertable x-ray probe into or adjacent to the tumor so as to deliver therapeutic radiation to the tumor. Alternatively, the x-ray probe may be inserted into a post-operative site, i.e. into the site where the tumor or a portion of the tumor was removed, so as to treat the tissue adjacent the site with a local boost of radiation. A serious problem in the treatment of cancerous tumors is the recurrence of tumorous growth after surgery. Frequently, even after surgical removal of a tumor, there is a high risk of recurrence of tumorous growth in the region surrounding the resected tumor. Many patients with recurrent tumors suffer tumor progression, i.e. metastasis. Such recurrent tumorous growth is due to the spread to tumorous cells around the operative site.
It is therefore desirable to reduce the risk of recurrent tumorous growth near or around the operative site, while at the same time preventing radiation damage to non-cancerous tissue.